Reinforced ceramic tile armor

ABSTRACT

A ceramic armor is disclosed that utilizes a titanium frame assembly surrounding monolithic ceramic tiles combined with aluminum pressure infiltration. The aluminum pressure infiltration serves to “wet” the ceramic, bonding the ceramic to the titanium frame on the top, bottom, sides and interior of the frame assembly. After aluminum pressure infiltration at high temperature followed by cooling, this combination creates compressive stress in all directions surrounding the ceramic thereby enhancing localization of a blast/projectile hit to enhance the armors effectiveness. Even after damage due to a projectile hit, adjacent tiles retain their structural integrity, residual stress, and bond to the frame assembly.

BACKGROUND

1. Field of Use

The present invention relates to ceramic armor produced by metallic encapsulation and structural reinforcement for increased structural integrity against blast/projectile hits.

2. Description of Prior Art

Ceramic containing armor has been shown to be an effective means to protect against a wide variety of ballistic threats because of its combination of high hardness, strength and stiffness along with low bulk density and favorable pulverization characteristics upon impact. Ceramic materials have long been considered for use in the fabrication of armor components because ceramic materials have a high hardness, are potentially capable of withstanding armor-piercing projectiles, and are relatively lightweight.

However, the use of ceramic materials in armor applications has been limited by the low impact resistance of these materials, which results from ceramic's brittleness and lack of toughness. Indeed, one of the significant drawbacks to the use of ceramic materials in armor applications is that they lack repeat hit capability. In other words, ceramic materials tend to disintegrate upon the first hit and cease to be useful when subjected to multiple projectiles.

For armor systems arranged in an array type structure, multiple projectile hits tend to disintegrate adjacent ceramics, propagating the hit throughout the structure. For a more effective utilization of ceramic materials in armor applications, it is necessary to improve the impact resistance of this class of materials.

Applicants have found that the use of a Titanium frame assembly surrounding monolithic ceramic tiles combined with aluminum pressure infiltration serves to “wet” the ceramic, bonding the ceramic to the titanium frame on the top, bottom, sides and interior of the frame assembly. After aluminum pressure infiltration at high temperature followed by cooling, this combination creates compressive stress in all directions surrounding the ceramic thereby enhancing localization of a blast/projectile hit to enhance the armors effectiveness. Even after damage due to a projectile hit, adjacent tiles retain their structural integrity, residual stress, and bond to the frame assembly.

Since the coefficient of expansion for titanium is higher than the CTE of the ceramic tiles, the cooling puts additional compressive stress on the ceramic tiles. In the present invention, the adjacent tiles are bonded to the top plate, bottom plate and side walls of titanium. So, when the middle tile is destroyed the surrounding tiles are still held in place and residual compression stress is maintained because the entire module is bonded into an integral structural system.

Prior art methods of construction such as the Hot Isostatic Pressure (HIP) process do not allow for adequate bonding of the ceramic to the frame assembly. The HIP process is where metal castings or other metal objects are squeezed at high temperature and high pressure to collapse any porosity present. Current titanium encapsulated, ceramic armor is made by fabricating a titanium structure with cavities, then placing ceramic tiles into the cavities. The HIP process heats the titanium encapsulated armor to about 950C and then pressurizes it to between 15,000 and 30,000 psi. This combination of heat and pressure softens the titanium and collapses the entire module, thus removing any gaps or porosity between the tiles and titanium, unlike the present invention. Then as the module cools the titanium shrinks.

In addition to not being able to control the defects (wrinkling, etc) inherent in the HIP process, the titanium does not bond to the ceramic tiles, and when the completed armor is struck by a projectile, the ceramic tile is shattered and reduced to rubble. The titanium walls surrounding that tile are not bonded to the surrounding tiles, so the residual compression that existed before the projectile impact is partially relieved for the adjacent, surrounding tiles.

SUMMARY OF THE INVENTION

The present invention relates to a ceramic armor utilizing a titanium frame assembly surrounding monolithic ceramic tiles combined with aluminum pressure infiltration. The aluminum pressure infiltration serves to “wet” the ceramic, bonding the ceramic to the titanium frame on the top, bottom, sides and interior of the frame assembly. After aluminum pressure infiltration at high temperature followed by cooling, this combination creates compressive stress in all directions surrounding the ceramic thereby enhancing localization of a blast/projectile hit to enhance the armors effectiveness. Even after damage due to a projectile hit, adjacent tiles retain their structural integrity, residual stress, and bond to the frame assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 shows a schematic cross-sectional representation of an armor construction encapsulating a plurality of ceramic tiles in accordance with the teachings of the present invention.

FIG. 2 illustrates a portion of the frame assembly used in the armor construction of FIG. 1. FIG. 3 illustrates the tiles that are fitted into the cells of the frame assembly of FIG. 2.

FIG. 4 is a top view of the frame assembly of FIG. 2 with the tiles of FIG. 3 fitted therein.

FIG. 5 is a bottom view of FIG. 4.

FIG. 6 is an exploded view of one embodiment of the armor construction in accordance with the teachings of the present invention.

DETAILED DESCRIPTION

In the following description, the same numerical references refer to similar elements. The embodiments, geometrical configurations, materials mentioned and/or dimensions shown in the figures or described in the present description are preferred embodiments only, given for exemplification purposes only.

In the context of the present invention, any equivalent expression and/or compound words thereof known in the art will be used interchangeably, as apparent to a person skilled in the art.

It is to be understood, as also apparent to a person skilled in the art, that other suitable components and cooperations therebetween, as well as other suitable geometrical configurations may be used for the armor construction according to the present invention, as will be explained herein and as can be easily inferred herefrom, by a person skilled in the art, without departing from the scope of the invention.

Furthermore, the order of the steps of the method described herein should not be taken as to limit the scope of the invention, as the sequence of the steps may vary in a number of ways, without affecting the scope or working of the invention, as can also be understood.

Referring to FIG. 6, which shows an exploded view of an embodiment of armor construction 10 made in accordance with the teachings of the present invention. As illustrated in FIGS. 2, 3 and 6, the armor construction includes a frame assembly 15 with ceramic plates or tiles 40 placed within the cells 17 of frame assembly 15. Frame assembly 15 includes side rails 15A and interior walls 15B connected together to form cells 17.

Side rails 15A include infiltration ports 15A1 where liquid infiltrant will enter under pressure. Referring to FIGS. 2 and 6, walls 15B include tabs 15B1 for engagement of top plate 20 slots 20A. A layer of Saffil paper 22 may be added between top plate 20 and tiles 40, and/or between backing plate 25 and tiles 40. Saffil paper 22 reduces the likelihood of residual stress cracking between the ceramic tiles 40 and titanium plates 20,25 placed upon tiles 40.

A Bottom plate 30 may be added between tiles 40 and backing plate 25. Bottom plate 30 facilitates the securement of tiles 40 within cells 17. In another embodiment of the present invention, the bottom plate 30 may be eliminated. In the preferred embodiment the frame assembly 15, top plate 20, backing plate 25, and bottom plate 30 are made of titanium. The walls 15B are titanium and at least 0.010 inches thick.

As illustrated in FIGS. 2 and 6, bottom plate 30 and top plate 20 includes slots 20A for engagement of tabs 15B1 located on the top and bottom of frame assembly 15. Tabs 15B1 are located on the top and bottom of walls 15B. A cross-section of the armor construction 10 of FIG. 6, in assembled form is illustrated in FIG. 1. Prior to being placed in an infiltration vessel armor construction 10 is welded by shield gas tungsten, electron beam or similar methods at tabs 15B1. The complete assembled armor construction 10 would be placed in an infiltration vessel or mold cavity then infiltrated with liquid metal.

The armor construction 10 should be heated in a vacuum or shielded with inert gas to prevent oxidation of the titanium surfaces. The gaps between ceramic tiles 40 and interior walls 15B, the gap between ceramic tiles 40 and top plate 20, and the gap between ceramic tiles 40 and backing plate 25, are at least 0.0005 inches, and preferably are between about 0.003 and about 0.008 inches.

The aluminum infiltration process causes aluminum to penetrate throughout the overall structure, filling the gaps between the aforementioned surfaces. The liquid aluminum wets the titanium and ceramic surfaces creating a bond between them when it solidifies. After solidification, bonding occurs throughout the armor construction, specifically between ceramic tiles 40 and interior walls 15B, between ceramic tiles 40 and top plate 20, and between ceramic tiles 40 and backing plate 25.

While molten aluminum is the preferred embodiment illustrated other suitable metals with a melting point below 900 degrees celcius maybe utilized that do not adversely react with titanium. A metal with a shear strength exceeding 25 MPa and a tensile strength exceeding 50 MPa is desirable as the bonding infiltrant. The infiltrating metal should react sufficiently to wet the surface of the titanium, but not so much that it creates a thick, brittle intermetallic reaction bond. The liquid metal infiltration process is described in U.S. Pat. No. 3,547,180 and incorporated herein by reference for all that it discloses.

In each of the embodiments of the present invention, it is preferred that the ceramic plate or tiles 40 are machined to be substantially the same width as walls 15B while allowing for tabs 15B1 to be raised enough above tiles 40 for engagement into slots 20A. In the preferred embodiment, only one tile fills cell 17, however, multiple tiles within each cell can be utilized. In the preferred embodiment, the layers of material components illustrated in FIG. 6 are symmetrical in length and width but not thickness.

It is preferred that the metal material used for frame assembly 15 consist of a material having relatively low density, high strength and good ductility along with a coefficient of thermal expansion higher than the coefficient of expansion for the ceramic tiles 40 encapsulated therewithin. Applicants have found that an alloy of Titanium known as Ti-6A1-4V or Ti-6A1-4V ELI (Extra Low Interstitials) is a suitable material for this purpose. Ti-6A1-4V has a relatively low density (4.5 g/cc), relatively high strength (900 MPa), and good ductility (yield strength of 830 MPa at 0.2% yield), and can be bought already annealed according to Mil T 9046 spec.

The thermal expansion of Ti-6A1-4V is about 10.5×10⁻⁶ in/in ° C. from 0-600° C., a coefficient considerably higher than that of dense SiC which has a thermal expansion coefficient of 4.1×10⁻⁶in/in ° C. from 0-600° C., a difference in which the thermal expansion coefficient for the Titanium alloy is over 2½ times the thermal expansion coefficient for the ceramic material.

In the preferred embodiment of the present invention, the ceramic material employed may consist of pressure assisted (PAD) SiC-N, one of a family of Coorstec dense hot pressed ceramics. Other grades and types of armor ceramics such as Silicon Carbide, Boron Carbide, Tungsten. Carbide, Titanium Diboride, Aluminum Oxide, Silicon Nitride and Aluminum Nitride or mixtures of the aforementioned materials can be employed. Such armor ceramics have thermal coefficients of expansion from about 3.0×10⁻⁶ to about 9×10⁻⁶ in/in ° C. and hardness greater than 1100 kg/mm².

There are several advantages to using Titanium as a surrounding frame assembly 15 material. First, the very high “yield” strength of Ti can be utilized to constrain the ceramic core very effectively and impede the material's disintegration. Herein, the important strength parameter is the “yield” strength of the surrounding Ti. When the armor package takes a hit, the ceramic core will tend to fracture and dimensionally expand due to opening cracks. In this situation, the surrounding metal will be forced to stretch out and the material's resistance to yielding will be an important factor in impeding the disintegration of the ceramic core. Ti-6A1-4V has a yield strength of at least 900 MPa. The higher the yield strength is the higher resistance against disintegration forces and provides a more effective constrain.

The unique combination of a high yield-strength titanium having an infiltrated bonding metal tends to constrain the ceramic within a cell after a projectile hit. After aluminum pressure infiltration at high temperature followed by cooling, this combination creates compressive stress in all directions surrounding the ceramic thereby enhancing localization of a blast/projectile hit to enhance the armors effectiveness. Moreover, bonding occurs throughout the armor construction, specifically between ceramic tiles 40 and interior walls 15B, between ceramic tiles 40 and top plate 20, and between ceramic tiles 40 and bottom plate 25.

Even after damage due to a projectile hit, adjacent tiles retain their structural integrity, residual stress, and bond to the frame assembly. It has further been observed that a damaged tile within a cell will not fully deteriorate within the cell after a projectile hit. Portions of the tile will remain bonded to the interior walls 15B, top plate 20, and bottom plate 25 even after a direct hit, due to the bonding of the metal infiltrant throughout the structure. The residual compression and integrity of the armor construction 10 may therefore be maintained in cells that have not yet been penetrated and the integrity of the armor construction 10 can be preserved for multiple hits.

Another advantage of Ti is the deformation mechanism by localized shear bands. In the case of ceramic encapsulation, the deformation of Ti will be limited to a very small portion of the Ti, which will in effect keep the substantial portion of the Ti intact. This will allow the Ti to preserve the constraining effect on the ceramic and improving its effectiveness. In the case of conventional metal and alloys, the deformation of metallic component propagates throughout the most the structure and as such distorts and deprives the constraining action necessary to improve the effectiveness of ceramic component. 

I claim:
 1. A ceramic armor comprising: a plurality of dense ceramic core tiles having a plurality of side surfaces, each of said plurality of dense ceramic core tiles having a top and bottom surface; an interconnected frame assembly, said frame assembly including an interior having a plurality of cells, said cells including a plurality of walls, said tiles disposed within said plurality of cells, said plurality of walls and said plurality of tile side surfaces having a gap therebetween of at least 0.0005 inches, said frame assembly further including side rails surrounding said plurality of cells, said side rails and said periphery of said plurality of cells having a gap therebetween of at least 0.0005 inches; at least one top plate and at least one backing plate having a top and bottom surface, said top plate bottom surface and said top surface of said plurality of dense ceramic core tiles having a gap therebetween of at least 0.0005 inches, said backing plate top surface and said bottom surface of said plurality of dense ceramic core tiles having a gap therebetween of at least 0.0005 inches; a metallic material encapsulating said plurality of cells, said top plate said backing plate, and said side rails, said metallic material infiltrating said gap between said plurality of said tile side surfaces and said plurality of cell walls forming a bond therebetween, infiltrating said gap between said side rails and said periphery of said plurality of cells forming a bond therebetween, infiltrating said gap between said top plate bottom surface and said top surface of said plurality of dense ceramic core tiles forming a bond therebetween, and infiltrating said gap between said backing plate top surface and said bottom surface of said plurality of dense ceramic core tiles forming a bond therebetween, wherein the CTE of said frame assembly, said top plate and said backing plate, is greater than the CTE of said plurality of said ceramic core tiles, said plurality of dense ceramic core tiles being under compressive stress.
 2. A ceramic armor as in claim 1, wherein said metallic material infiltrant has a shear strength exceeding 25 MPa, a tensile strength exceeding 50 MPa, and a melting point less than 900 degrees celcius.
 3. A ceramic armor as in claim 1, wherein said frame assembly, said top plate and said backing plate are titanium.
 4. A ceramic armor as in claim 3, wherein the CTE of said frame assembly, said top plate and said backing plate is at least 2.5 times greater than the CTE of said plurality of said ceramic core tiles, said plurality of dense ceramic core tiles being under compressive stress.
 5. A ceramic armor as in claim 3, wherein said yield strength of said titanium is at least 900 MPa.
 6. A ceramic armor as in claim 5, wherein said yield strength of said titanium frame assembly is increased with said metallic material bonding, said bonding of said metallic material throughout said ceramic armor preserving said compressive state of said plurality of tiles adjacent to a projectile hit.
 7. A ceramic armor as in claim 3, wherein said titanium walls are at least 0.010 inches thick.
 8. A ceramic armor as in claim 5, wherein said side rails further include ports for the distribution of said metallic infiltrant throughout the ceramic armor.
 9. A ceramic armor comprising: a plurality of dense ceramic core tiles, having a plurality of side surfaces each of said plurality of dense ceramic core tiles having a top and bottom surface; an interconnected frame assembly, said frame assembly including an interior having a plurality of cells, said cells including a plurality of walls, said tiles disposed within said plurality of cells, said plurality of walls and said plurality of tile side surfaces having a gap therebetween of at least 0.0005 inches, said frame assembly further including side rails surrounding said plurality of cells, said side rails and said periphery of said plurality of cells having a gap therebetween of at least 0.0005 inches; a metallic material encapsulating said plurality of cells, and said side rails, said metallic material infiltrating said gap between said plurality of said tile side surfaces and said plurality of cell walls forming a bond therebetween, infiltrating said gap between said side rails and said periphery of said plurality of cells forming a bond therebetween.
 10. A ceramic armor as in claim 9, further including: at least one top plate and at least one backing plate having a top and bottom surface, said top plate bottom surface and said top surface of said plurality of dense ceramic core tiles having a gap therebetween of at least 0.0005 inches, said backing plate top surface and said bottom surface of said plurality of dense ceramic core tiles having a gap therebetween of at least 0.0005 inches; a metallic material encapsulating said at least one top plate and at least one backing plate, said metallic material infiltrating said gap between said top plate bottom surface and said top surface of said plurality of dense ceramic core tiles forming a bond therebetween, and infiltrating said gap between said backing plate top surface and said bottom surface of said plurality of dense ceramic core tiles forming a bond therebetween.
 11. A ceramic armor as in claim 9, wherein said metallic material infiltrant has a shear strength exceeding 25 MPa, a tensile strength exceeding 50 MPa, and a melting point less than 900 degrees celcius.
 12. A ceramic armor as in claim 10, wherein said frame assembly, said top plate and said backing plate are titanium.
 13. A ceramic armor as in claim 12, wherein said yield strength of said titanium is at least 900 MPa.
 14. A ceramic armor as in claim 9, wherein said yield strength of said frame assembly is increased with said metallic material bonding, said bonding of said metallic material throughout said ceramic armor preserving said compressive state of said plurality of tiles subsequent to a projectile hit.
 15. A ceramic armor as in claim 12, wherein said titanium walls are at least 0.010 inches thick.
 16. A ceramic armor as in claim 9, wherein the CTE of said frame assembly is greater than the CTE of said plurality of said ceramic core tiles, said plurality of dense ceramic core tiles being under compressive stress.
 17. A ceramic armor comprising: a plurality of dense ceramic core tiles having a plurality of side surfaces, each of said plurality of dense ceramic core tiles having a top and bottom surface; an interconnected frame assembly, said frame assembly including an interior having a plurality of cells, said cells including a plurality of walls, wherein said walls are at least 0.010 inches thick, said tiles disposed within said plurality of cells, said plurality of walls and said plurality of tile side surfaces having a gap therebetween of at least 0.0005 inches, said frame assembly further including side rails surrounding said plurality of cells, said side rails and said periphery of said plurality of cells having a gap therebetween of at least 0.0005 inches; at least one top plate and at least one backing plate having a top and bottom surface, said top plate bottom surface and said top surface of said plurality of dense ceramic core tiles having a gap therebetween of at least 0.0005 inches, said backing plate top surface and said bottom surface of said plurality of dense ceramic core tiles having a gap therebetween of at least 0.0005 inches; wherein said frame assembly, said top plate and said backing plate are titanium, said titanium having a yield strength of at least 900 MPa; a metallic material encapsulating said plurality of cells, said top plate, said backing plate, and said side rails, wherein said metallic material has a shear strength exceeding 25 MPa, a tensile strength exceeding 50 MPa, and a melting point less than 900 degrees celcius, said metallic material infiltrating said gap between said plurality of said tile side surfaces and said plurality of cell walls forming a bond therebetween, infiltrating said gap between said side rails and said periphery of said plurality of cells forming a bond therebetween, infiltrating said gap between said top plate bottom surface and said top surface of said plurality of dense ceramic core tiles forming a bond therebetween, and infiltrating said gap between said backing plate top surface and said bottom surface of said plurality of dense ceramic core tiles forming a bond therebetween; wherein the CTE of said frame assembly, said top plate and said backing plate, is at least 2.5 times greater than the CTE of said plurality of said ceramic core tiles, said plurality of dense ceramic core tiles being under compressive stress; wherein said yield strength of said titanium frame assembly is increased with said metallic material bonding, said bonding of said metallic material throughout said ceramic armor preserving said compressive state of said plurality of tiles subsequent to a projectile hit.
 18. A ceramic armor as in claim 1 wherein said bonding infiltrant is aluminum. 